1. Field of the Invention
The present invention generally relates to the field of photography and, more specifically, to photographic processing apparatus by which the thickness of a layer of processing fluid is controlled in a uniform manner as the processing fluid is spread across preselected portions of an integral type self-processable film unit.
2. Description of the Prior Art
In the processing of self-processable type film units, an important and well-known step by which a latent image is transformed into a visible one involves spreading a viscous processing fluid containing chemical agents between preselected layers of the film unit and substantially coextensive with the photoexposed area to initiate a diffusion transfer development process which provides a visible transfer image. To assure that the resultant visible image from the diffusion transfer process meets high standards of photographic quality and that each part of the latent image receives equal treatment, it is necessary that the thickness of the processing fluid layer over the film units photoexposed area be substantially uniform and at least meet a minimum thickness requirement.
The primary concern of the present invention is with the structure and function of a photographic processing apparatus which can be used with integral type self-processable film units to compensate for certain fluid spreading phenomena which would otherwise result in a nonuniformly thick fluid layer or, under extreme temperature conditions, an incompletely covered photoexposed area.
The integral type film units with which the present invention is most useful contain all the photographic components necessary for the diffusion transfer process and are described in considerable detail, for example, in U.S. Pat. Nos. 3,415,644; 3,594,165; and 3,761,268. Typically, these film units comprise, in general terms, a pair of superposed sheet elements, at least one being transparent, which serve to support layers of chemical substances which usually comprise photosensitive and image-receiving layers; and, as well, include a rupturable container of the viscous processing fluid positioned adjacent a leading edge of the film unit and adapted to have its fluid contents spread between the sheet elements to initiate the diffusion transfer process. The sheet elements and the rupturable container are typically held together by a binding element which is wrapped around their lateral edges and also functions to provide a mask which defines the area of the photosensitive layer which can be photoexposed. Exposure of the film unit's photosensitive layer is generally done through the film unit's transparent sheet, and it is also through the transparent sheet that the visible transfer image is viewed after the diffusion transfer process is complete.
Such film units are usually used with fully automatic cameras which expose them in a well-known manner and afterwards advance them from their exposure location into engagement with a processing apparatus. The processing apparatus which forms an integral part of the camera then continues the advancement of the film unit toward the outside of the camera and during advancement applies a pressure lengthwise of the film unit. The pressure during this operation first ruptures the container of processing fluid causing its fluid contents to be released as a generally elongated mass extending widthwise of the film unit's exposed area and adjacent the film unit's leading edge and then causes the released mass of processing fluid to flow between the sheet elements, opposite to the direction of advancement of the film unit through the processing apparatus, so that the widthwise distributed mass of processing fluid is progressively deposited in a layer lengthwise of the film unit's exposed area.
It is during this fluid spreading step of the diffusion transfer process that certain complex fluid flow phenomena occur which tend to cause the thickness of the layer of processing fluid to be nonuniform over the film unit's exposed area. In general, the phenomena which tend to cause the fluid to spread so that its thickness is nonuniform are related to the mechanical structure and properties of the film unit, interactions between the film unit and the processing apparatus during the fluid spreading phase, and the manner in which the film unit is advanced into engagement with the processing apparatus.
For example, the manner in which the film unit's components are bound together has been found to influence uniformity. In particular, because the sheet elements are tightly bound along their lateral edges, it has been found that there is generally more lengthwise resistance to fluid flow along these edges than there is to fluid which flows lengthwise along the center of the film unit's exposure area. As a consequence, the thickness of the fluid layer over the central regions of the exposure area tends to be generally greater than that over the exposure area's lateral regions.
The prior art discloses processing apparatus for correcting this tendency toward a centrally thickened layer of processing fluid over the film unit's exposure area. More particularly, U.S. Pat. No. 3,776,118 issued to John J. Driscoll et al on Dec. 4, 1973 and entitled "Photographic Film Processing Apparatus" discloses a processing apparatus comprising a pair of processing rollers one of which is crowned to provide it with a predetermined convex profile configuration by which the thickness of the layer of processing fluid over central regions of the film unit's exposure area is thinned out.
Also the tendency for thicker processing fluid layers at the center of the exposure area can be aggravated if the processing apparatus has rollers which bend during the fluid spreading step. This usually happens when the rollers are intentionally made light weight to reduce their inertia so that less power is required to drive them in the case where they are automatically driven by a motor and gear train arrangement. The crowned roller is therefore of use to compensate for any roller bending which may occur as a result of the pressures they experience during fluid spreading.
Although the "crowned" roller represents a solution to the nonuniformity problem outlined above, it suffers from the disadvantage of being relatively expensive to manufacture. A less expensive alternative to the "crowned" roller, which is disclosed in Great Britain patent specification No. 1,486,846 published on Sept. 28, 1977 in the name of Fuji Photo Film Co., Ltd. and entitled "Film Unit Processing Means," comprises a processing apparatus having a pair of juxtaposed rollers mounted so that their axes of rotation are crossed to provide an effect similar to that achieved with the "crowned" roller.
In addition to the foregoing solutions to this particular nonuniformity problem, it has also been found that deflecting the film unit out of its normal path of travel after it emerges from between the processing rollers can have a beneficial influence on uniformity. Processing apparatus by which deflection can be achieved is respectively taught and disclosed in U.S. Pat. No. 3,810,211 issued to Richard R. Wareham et al on May 7, 1974 and entitled "Self-Developing Camera System" and U.S. Pat. No. 3,994,002 issued to Andrew S. Ivester on Nov. 23, 1976 and entitled "Self-Developing Camera With Film Unit Deflecting Structure."
Another source of nonuniformity in the thickness of the fluid layer comes about when the film unit is advanced in a canted manner into engagement with the processing apparatus. Unlike the previous nonuniformity problem, however, this particular one is more localized in that it manifests itself as an incomplete coverage problem at one corner of the film unit's trailing edge.
To be more specific, the fully automatic cameras with which these film units are used are generally provided with a film advancing mechanism to automatically move the film units from their exposure position into engagement with the processing apparatus. The film advance mechanisms, which are well-known, usually have a "pick" arm which engages only one side of the film unit's trailing edge to provide a force which moves the film unit toward the processing apparatus (see, e.g., U.S. Pat. No. 3,709,122). Because the "pick" applies its force in an asymmetric fashion, the film unit moves toward the processing apparatus with its leading edge canted at a predetermined angle with respect to its general direction of travel. It has been observed that the film unit is maintained in this canted attitude as it travels through the rollers of the processing apparatus. With these one-sided "picking" arrangements, there is a tendency for the corners of the exposure area adjacent the pick side of the film unit's trailing edge to be incompletely covered by processing fluid as required, particularly at depressed operating temperatures where the viscosity of the processing fluid is higher.
One explanation for this incomplete corner coverage problem is that the canting may give rise to a lateral (widthwise) force component that causes the processing fluid to flow to the non-pick side of the exposure area. Based on this explanation, the prior art provided a solution in the form of a processing roller having a reduced end diameter on the "pick" side to obviate this tendency. The reduced end diameter causes a reduction in the thickness of the processing fluid in regions adjacent the "pick" side so that the coverage capability of the fluid is extended in those regions to eliminate the tendency for the "pick" side to be incompletely covered with processing fluid (see U.S. Pat. No. 3,854,809 issued to John J. Driscoll, Dec. 17, 1974 and entitled "Photographic Apparatus").
Another explanation for this tendency is discussed in U.S. Pat. No. 4,020,498 issued to Harvey S. Friedman on Apr. 26, 1977 and entitled "Photographic Fluid Processing Apparatus." Here, it is reasoned that the incomplete corner coverage problem comes about as a result of the detailed interactions which take place between a pair of spaced apart annular grooves, located in one of the rollers, and the longitudinally bound margins of the film unit as the canted film unit is advanced lengthwise through the rollers. Because the film unit is canted, its interaction with the annular grooves is also asymmetric, a condition not intended. This condition causes the fluid which is available for the regions of the exposure area adjacent the "pick" side to be deposited at a faster rate than intended thereby causing a deficit to exist when the "pick-side" corner is ready to be covered. The Friedman patent provides a solution by positioning the annular grooves located on one of its rollers in an asymmetric manner to compensate for the canted attitude of the advancing film unit.
The prior art also discloses in U.S. Pat. No. 4,016,578 issued to Harvey S. Friedman on Apr. 5, 1977 and entitled "Processing Fluid Flow Control Device For Self-Developing Camera" a processing apparatus having a specially contoured camming surface for intercepting a film unit as it emerges from a pair of processing rollers to provide the film unit with a complex curvature which influences the thickness distribution of the layer of processing fluid--particularly along both sides of the exposure area.
Because processing apparatus of the foregoing type, found in the prior art, represent a significant part of the cost of the cameras in which they are used, it is a primary object of the present invention to provide a less expensive processing apparatus for use in automatic cameras which utilize one-sided film advance arrangements and the foregoing type integral type self-processable film units and by which both types of fluid thickness nonuniformities discussed above can be eliminated.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements, and arrangement of parts which are exemplified in the following detailed disclosure.